Within both industrial settings and everyday households, carrying heavy loads up and down stairs is cumbersome and may even pose a potential safety hazard. Unfortunately, existing solutions for traversing stairs have significant shortcomings.
Material handling devices, such as hand trucks, carts and dollies, are frequently used to assist in carrying loads up and down stairs. However, these devices require the payload to be tilted in order to balance the center of mass, and must be stabilized by the human operator.
Similarly, mobility devices for the elderly, disabled or infirm, such as wheelchairs and motorized scooters, are generally designed to operate on a level surface. To traverse stairs, these devices generally require ramps or the assistance of another person.
Stairs are a significant barrier for mobile robots, particularly those intended for domestic applications. For example, the Roomba vacuum cleaner, which is intended to automate the task of vacuuming, lacks the ability to traverse stairs and must be manually carried from one level of the house to another. Other robots rely on tank-like treads, which require the payload to tilt, or use anthropomorphic legs, which necessitate an extremely complex and expensive solution.
Presently, various designs of stair traversing devices with level-keeping capabilities have been put forth in the prior art. Some are implemented in the form of coordinated walking elements or a series of articulating wheel sets, while others are implemented in the form of a robot with feedback control.
US Patent Publication No. US 2014/0326521 discloses one such solution that relates to a transport device comprising a load carrying body, at least one central walking element, a first side walking element and a second side walking element. At least one central walking element is arranged in-between the two side walking elements. The walking elements are arranged at the load carrying body in a manner to be capable of moving up and down with respect to the load carrying body, wherein the side walking elements can move up and down independently from the central walking elements by means of vertical actuators. Also, the walking elements are arranged at the load carrying body in a manner to be capable of moving back and forth in horizontal direction with respect to the load carrying body, wherein the walking elements can move back and forth independently from the central walking elements by means of horizontal actuators.
U.S. Pat. No. 7,677,345 discloses another solution in the form of a mobile, wheeled robot. In particular, the '345 Patent discloses a moving robot of narrow footprint, having quick traveling performance on a plane-surface, as well as an anti-tumbling function. The robot is able to cope with travel over surfaces with level differences by means of its wheel arrangement. In front and rear of main driving wheels, each being controlled through the inverted pendulum control, are disposed supporting legs, tips of which can be lifted up and down, wherein the tips of the supporting legs are positioned to keep a predetermined distance between a traveling surface, when running on the inverted two-wheels travel, and the supporting legs are fixed or either one in the fall-down direction is thrust out into the fall-down direction, so as to protect it from falling down. Further, upon the basis of detection information of floor-surface distance sensors and side-surface distance sensor, which are provided at the tips of the supporting legs, the robot senses an existence of a level difference and/or an inclined surface, so as to let the supporting legs to escape from the level difference and/or the inclined surface, and holds the position of gravity center thereof, stably, through other one of the supporting legs, being landed on the ground, and the main driving wheels; thereby enabling to travel over the level difference and the inclines surface.
Yet another stair-climbing apparatus is disclosed in U.S. Pat. No. 8,776,917. The patent discloses a stair-climbing apparatus that has a series of articulating wheel sets extending below a load carrying platform. All of the wheel sets are vertically adjustable to negotiate stairways and similar changes of elevation. The lead wheel set is fixed longitudinally relative to the platform, while following wheel sets are longitudinally adjustable to adjust for the pitch or slope of different stairways. The apparatus uses sensors e.g., mechanical, infrared, ultrasonic, etc. to detect the presence of the stair risers and their height, control of the assembly being accomplished by a control circuit on board the machine. The wheel sets are raised and lowered independently of one another by pantograph mechanisms extending between the platform and the wheel sets. The horizontally adjustable wheel sets are positioned by a longitudinally disposed rack on the platform.
The devices disclosed in the prior art, such as the ones identified above, may rely on either a plurality of moving components that may be driven by multiple actuators. Further, the prior art devices may require active control involving complex control logic in order to traverse the stairs while remaining level. These features generally result in large, complex electro-mechanical devices that require multiple moving components working under synchronized control. Greater complexity generally increases the likelihood of error and failure, and typically results in higher manufacturing and maintenance costs. Thus, there is a need for smaller, simpler and purely mechanical stair traversing device that remains stable and level without the need for active electronic control.